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I see, so the shell momentarily switches its STDOUT from the terminal to STDIN for the cat process. then all the rest of the pipe stuff happens, then the shells points its 1 (STDOUT) back to the terminal. And also because processes cat and php are involving IO then they definitely must have file descriptors!

the_velour_fog
– the_velour_fog

2016-05-21 04:10:08 +00:00
Commented May 21, 2016 at 4:10
The process that calls exec, in this case the shell, does close and open the file descriptors so they correspond to what is needed in the child process.

Julie Pelletier
– Julie Pelletier

2016-05-21 04:12:21 +00:00
Commented May 21, 2016 at 4:12

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